Biological determinants of spontaneous late preterm and early term birth: a retrospective cohort study.

Objective: Our aim was to examine the association between biological determinants of preterm birth (infection and inflammation, placental ischaemia and other hypoxia, diabetes mellitus, other) and spontaneous late preterm (34-36 weeks) and early term (37-38 weeks) birth.

Design: Retrospective cohort study.

Setting: City of London and Middlesex County, Canada.

Sample: Singleton live births, delivered at 34-41 weeks to London-Middlesex mothers following spontaneous labour.

Methods: Data were obtained from a city-wide perinatal database on births between 2002 and 2011 (n = 17,678). Multivariable analyses used multinomial logistic regression.

Main Outcome Measure: The outcome of interest was the occurrence of late preterm (34-36 weeks) and early term (37-38 weeks) birth, compared with full term birth (39-41 weeks).

Results: After controlling for covariates, there were associations between infection and inflammation and late preterm birth (aOR = 2.07, 95% CI 1.65, 2.60); between placental ischaemia and other hypoxia and late preterm (aOR = 2.21, 95% CI 1.88, 2.61) and early term (aOR = 1.25, 95% CI 1.13, 1.39) birth; between diabetes mellitus and late preterm (aOR = 3.89, 95% CI 2.90, 5.21) and early term (aOR = 2.66, 95% CI 2.19, 3.23) birth; and between other biological determinants (polyhydramnios, oligohydramnios) and late preterm (aOR = 2.81, 95% CI 1.70, 4.64) and early term (aOR = 1.89, 95% CI 1.32, 2.70) birth.

Conclusions: Our findings show that delivery following spontaneous labour even close to full term may be a result of pathological processes. Because these biological determinants of preterm birth contribute to an adverse intrauterine environment, they have important implications for fetal and neonatal health.